This invention relates to tires for vehicles which generally have at least one wheel at each corner such as passenger cars, vans, trucks or buses.
In common with most other types of tires, in order for this tire to perform well under all conditions it is usual for the ground contacting tread region of the tire to be provided with relatively deep grooves in the surface.
In wet conditions such grooves assist in clearing water from the contact area between the tire tread and the road surface and thus help to retain steering control of the vehicle by preventing aquaplaning. In other conditions such as snow and ice or in off-road applications such grooves provide edges which assist in the transmission of traction forces.
However the provision of such grooves effectively weakens the tire tread and renders it more prone to wear. This occurs because such grooves divide the tread into discrete elements such as ribs and blocks which individually are more susceptible to deformation and movement in the tire/ground contact region due to the tractive forces transmitted therein resulting in abrasion of the rubber against the road surface.
In making the present invention, the inventors studied the alignment of the grooves in the tread of such tires and determined that it was possible to arrange these so as to minimize wear of the tread rubber.
Accordingly it is an object of the present invention to provide a tire for a four wheeled vehicle which is improved in tread wear.
According to one aspect of the present invention a tire for a vehicle having at least one wheel at each corner comprises a ground contacting tread extending axially between first and second edge regions and having tread grooves formed therein, wherein in the first axial edge region of the tread the tread grooves are aligned substantially in the tire circumferential direction and in the second axial edge region of the tread the grooves are aligned substantially in the tire axial direction and in a third axial region of the tread axially between the first and second edge regions the alignment of the grooves changes progressively from circumferential to axial.
According to another aspect the invention provides a tire mounted on a vehicle, the tire comprising a ground contacting tread extending between first and second axial edge regions and having tread grooves formed therein, the first axial edge region of the tread the tread grooves are aligned substantially in the tire circumferential direction and in a second axial edge region of the tread the grooves are aligned substantially in the tire axial direction and in a third axial region of the tread axially between the first and second edge regions the alignment of the grooves changes progressively from circumferential to axial and the first axial edge region of the tire is disposed nearest to the vehicle longitudinal centerline.
According to yet another aspect the invention provides a method of determining the required tread groove angle to form the tread pattern of a tire for a four-wheeled vehicle to give optimum tread wear comprising at successive axial points across the tread from the center to the tread edge aligning the tread groove in the direction of the resultant force acting on the tread at that axial point when the point is in the tire/road contact region.